The long term goals of this research are to understand synaptic plasticity and sensory-motor processing in the electrosensory lobe of mormyrid electric fish. The electrosensory lobe is a cerebellum-like structure which receives the primary afferent input from electroreceptors. The lobe is also strongly affected by descending input from other central structures. One of the most prominent of these inputs is an electric organ corollary discharge (EOCD) signal associated with the motor command that drives the electric organ to discharge. Many EOCD effects on cells of the electrosensory lobe are plastic and depend upon previous sensory input. Evidence indicates that the plasticity is due to changes in synaptic efficacy within the lobe. The experimental work will be done in the slice preparation and most of the studies will make use of intracellular recording. This proposal has 5 Specific Aims: 1) To determine the synaptic site(s) of EOCD plasticity and to measure its temporal properties in vitro. Certain hypotheses will be tested concerning the site of plastic change. These hypotheses have been derived from in vivo work and include the hypothesis of plastic change at inhibitory synapses. 2) To determine the transmitters and receptor subtypes at the synapses which show plastic change. Inhibitory and excitatory responses will be elicited by artificial electrical stimuli. These responses will be examined for the effects of antagonists to different subtypes of receptors. Agonists will also be tested. 3) To determine the identity and role of the broad dendritic spikes. Broad dendritic spikes which are probably calcium spikes appear to have a role in EOCD plasticity. The role of these spikes in plasticity, the identity of these spikes as calcium spikes, and the role of calcium in EOCD plasticity will be investigated. 4) To complete our knowledge of the morphology of the electrosensory lobe. Morphological work will be done on both cell morphology and connectivity. Studies of the mormyrid electrosensory lobe are expected to contribute to our general knowledge of synaptic plasticity and the role of such plasticity in perceptual and sensory-motor processes.